Recently, digital video cameras having a function to transmit and receive a digital video signal and a digital audio signal by use of IEEE 1394 high-speed serial bus (hereinafter simply referred to as 1394 serial bus) have already been commercially available on the market. Also, the 1394 serial bus receives a remarkable attention as an interface for connecting peripheral equipment to a personal computer.
This 1394 serial bus may prepare an isochronous transfer mode for assuring that packets of a predetermined amount may be transmitted and received at every 125 .mu.s and an asynchronous transfer mode suitable for transferring control commands and files although the asynchronous mode is inferior to the isochronous transfer mode in priority. For example, when digital electric household appliances such as digital video camera and a digital video deck may be connected by the 1394 serial bus, there can be transferred at a high speed real time data such as a digital video signal and a digital audio signal.
A communication system 200 connected to the electric household appliances by this kind of 1394 serial bus will be described with reference to FIG. 13. The communication system 200 shown in FIG. 13 may include a digital satellite receiver (Integrated Receiver Decoder: hereinafter referred to as an IRD receiver) 1 to receive digital satellite broadcasting such as a movie and a piece of music. A mini disc 2 may be connected to this IRD receiver 1 by the 1394 serial bus 6A to record/reproduce digital data such as a piece of music received from the satellite.
Also, digital home video apparatus (hereinafter referred to as D-VHS apparatus) 3 may be connected to the IRD receiver 1 by a 1394 serial bus 6B in a daisy-chain fashion (daisy chain fashion) to record/reproduce digital data such as a piece of music received from the satellite. A digital video deck (hereinafter referred to as a DV deck) 4 may be connected to the D-VHS apparatus 3 by a 1394 serial bus 6C in a daisy-chain fashion to record/reproduce digital data such as recording video data. A video recorder having a built-in type camera (hereinafter referred to as a DV camera/recorder) 5 may be connected to the DV deck 4 by a 1394 serial bus 6D in a daisy-chain fashion to record/reproduce digital data such as recording video data.
MPEG transport stream data (hereinafter referred to as MPEG data) based on the moving picture compression system may be transferred among the IRD apparatus 1, the mini disc 2 and the D-VHS apparatus 3, and digital video data (hereinafter referred to as DV data) may be transferred between the DV deck 4 and the DV camera/recorder 5. For example, in the communication system 200 shown in FIG. 13, the digital video signal and the digital audio signal recorded by the DV camera/recorder 5 may be played back and these DV data may be recorded by the DV deck 4.
According to the conventional communication system 200, when digital household equipment for handling MPEG data and DV data having different signal formats may be connected to the 1394 serial buses 6A to 6D, the DV camera/recorder 5 which had been served as a digital video signal output machine, for example, to issue a bus use request and which had acquired the bus use right may output a digital video signal to a default channel No. (e.g. channel 63) on a previously-prescribed bus management.
Then, the DV deck 4 which, may be used as the digital video signal input machine may input a digital video signal from the same default channel No. Thus, the digital video signal can be easily transmitted and received between the DV camera/recorder 5 and the DV deck 4 which had acquired the bus use right with the priority to the IRD receiver 1 used as the output machine.
However, according to the conventional communication system 200, if the DV camera/recorder 5 and the DV deck 4 shown in FIG. 13 may use the 1394 serial bus 6D which is the specific interval in which they had previously acquired the bus use right with the priority to digital household equipment which can become other output machines, the IRD receiver 1 and the mini disc 2 cannot use the 1394 serial bus 6A and the IRD receiver 1 and the D-VHS apparatus 3 cannot use the 1394 serial bus 6B.
The reason for this may be considered such that DV data may enter the 1394 serial buses 6A to 6C for which the DV camera/recorder 5 and the DV deck 4 have not issued the bus use requests so that the IRD apparatus 1, the mini disc 2 and the D-VHS apparatus 3 which may handle MPEG data cannot receive the DV data.
Therefore, although the 1394 serial buses (hereinafter referred to as communication control buses) 6A and 6B have sufficient available channels and bandwidths (bus resources) to handle MPEG data, such available channels and bandwidths cannot be used between the IRD receiver 1 and the mini disc 2 and the IRD receiver 1 and the D-VHS apparatus (hereinafter referred to as electronic device) 3. In this connection, it may become difficult to record a piece of music or the like digitally received at the IRD receiver 1 from the satellite on the mini disc 2 or to record a movie received at the IRD receiver 1 on the D-VHS apparatus 3 at the same time DV data may be recorded on the DV deck 4 from the DV camera/recorder 5.
As a result, there arises a problem that applications that can input and output signals on the communication system 200 may be limited, thereby making it impossible to utilize the bus resource effectively.
Therefore, in view of the above-described aspect, the present invention is created and, an object of the present invention is to provide a communication control method, a communication system and electronic devices used therefor in which even when signal formats of data used on the communication control bus are different from each other, communication control buses of other specific intervals in which use requests are not overlapped can be simultaneously used by other electronic devices and the communication control bus can be utilized effectively.